Machine for joining sheet materials by the heating effect of electric stress alternating at high frequency



y 1949- J. c. QUAYLE ET AL 2,477,313

MACHINE FOR JOINING SHEET MATERIALS BY THE HEATING EFFECT OF ELECTRIC STRESS ALTERNATING I AT HIGH-FREQUENCY Filed (mp9, 1946 C j-W Patented July 26, 1 949 MACHINE EORJOINING SHEEEMAIERIAIZS BY THE. HEATING. EFFECT," OF EIJ'EC'IRIIIX STRESS ALTERNATINGL AT HIGH FRE- QUENCY 'ApplicatiorrOctobenQ, 1946; Serial No. 7023220 In:.:Great-Britain October 25,19451 1. Claim.. 1

Tlieinvent-ionq is; concerned withmachinesv to bezusedzforrjoiningrsheet materials utilising the heating; effect: on: the materials of electric stress alternatinga-t highjfrequency by which the materialfis softened-,1 and rendered adhesive so that; twnisllmrimposedtlayers pressed together locally imthepmachinei-are J'oinedat the region or-line. oilip ressurei, Such machines carry out operatimezoneappropriatasheet materials of a kind sim'flan-tolthose performed by a sewing machine (wittk. .the-;diff erence thattheapplication of heat amt pressure; isused tomake a seam instead of stitehingyltandare accordingly, structurally simie larztonsewinggmachinesinthat they possess a workta-ble; Orr-which the materials to be treated are spreadandcover which they are fed as the seaming proceedst and-haveopgrrative parts helowi-thesworktable ,and coeactingoperative parts; aboveithe table, the upper parts being. supported by;aastandardrproiectingupward from the table at a distance from the operative point andga hori. zonta-l:armtoverhangingvthe tablefrom the standard togtherworkinglpoint. The method of manipulatiomof; the; material on" the machinev is also:v similar toqthat, employed with a sewing: machine;

The; pressure isapplied by rollers, theone-car:- riede above-the material on the worktable and; theaotherrcarried; below the material. They are. preerab1y.bethdriven. Onerof them, usually the.

gp o e is-,. yie1d-ing-ly mounted under spring pressure; The electric-field forheating the materiaL-is applied by means of electrodes one'placed above the. material and one or more below; These electrodes may be provided wholly or. in. artiby. thepressure; rollers.

The .-'joining- .isefiected; for'instanceqas a seam; between-two-sheetsof material, by heating the sheets to the soft: adhesive state on the contacting surfaoeswhile-pressing them together between. thesrollers and. thus causing the two sheets to coalesce along thevline of treatment. During this treatment: the materials are carried forward; steadily; by-.therollers sothat the material passes. quickly into the heating and pressure-regionand I then quicklyaou-t; of it into a region where the; L

efiect: ofi theatmosphere' operatesupon theejoined. surfaces so that they remain: strongly adheringi. The: alternating electric; stress in the material:; between the. I electrodes is obtained by establishing;ate-potential diiference between these electrodesbyconnecting themappropriately with ashigh frequencyoscillator.

operating conditions: of a. piece of work: vary, considerably due, for instance to 2f differences my speed: Qff: practical; operation; beetween. straight-irons; and turns-:andhetween iotherz features of, the work and. imsome-1caseswdneto: differences inthe natureof 1' the :material: where thisiis not:uniformzthroughout; Operatinsxcomditionslalsovary; Hormones-piece of worlato. an; other; for: instance due to. diffierencesgin $13116 ens. tu'retottheimaterials. andiinvtheir. thickness;.. present-:inventiomprovidesgcontrol arran ements; whereby; these conditions. are: dealt": with: in; as convenient and advantageous: manner securin satisfactory joining of; the materials throughout? anda high average speed of working The. controlof the; conditions during running:

= is-..in; accordance-with; theeinventiorrlexertedr as.

singlemember;preferably'footroperated:which-is. made .to adjustsimultaneouslyandizinstheesamey sensepthe speed: of 1 the-5 I'011BIS)dIil/ih8li thee-mates" rial forward; and 'bhB-rhiEh. frequency powenrsu-pe plied to the; electrodes:v Ass the; speeds increases; the voltage applied; to;, the;- electrodes; azlsozxrises; and inethat Way, :the.:.rate-. of zheatingz; is: increased so; thatkthef material in; itsgshorter; time; of;- pas. sa e paststheelectrodesxand pressure members:-

is -raisedtto. the requireditemperature. fonanlefa fective; joining; The relationa-betweenaspeediott rollers-1 and:v high; frequency power: may: be:-. dif ferent for different; pieces of work: This: is; takeni care; of; by, :the providing: for: anti overrid ing;.,controli-:for one ,of;the factors preferably the high .1 frequency voltage-.- which: cam be: set-:.beiore-.- commencementzoi: the .worla'and is. automatically effective until. changed...

The .COIltIZOla maypfor instance; beaexerted: by:

J I two; rotary switches.conpledgtogether: andoper a-ted by;arfootpedal,one=contro1ling;;the-moton as;

by; rheostat;.and:: the. other: the voltage oi: the high: frequencyoutput; as: by;- a; variable: transforlmerzin th sunplyrotpowenrfrom; themains tot the oscillatorn The --overriding controlsmay be provided. by: adjustment: of the-. ratios. at? gearing. together of theitwozrotary switches:

The-:invention-= isxfurther: described hereinafter at with reference, by way of example, to the--ae- .companyingt drawing; which. is a diagrammatic representation lofvatmachine; havingvcontroli: artran-garmentsv inaccordance. with the. invention-..

Themachine: comprises a work-table: hon .whicha. the .materials .rtoe-bes treated are spreadeand-govers which they, are fed. as the), seaminga proceeds Pressure. is, appliedv by; rollers, one-.-r,ol1er= 2- sup ported abovethe. worktablel and..the.. other. 3;" supported .belowithe materia1. Bothtrollers Land 3i are: positively. driven. by; an? electric motorzk...

changes. in the. number or layers to. be. joined, as Thamotor leidrivesiazzshattl 5 throushoreductiom gearing 6. on one end of the shaft is fixed the lower roller 3, and on the other end of the shaft is a bevel gear whereby through transmission gearing the drive is supplied to the upper roller 2. The upper roller is supported in the end 8 of a horizontal arm 9 which overhangs the worktable I from a standard It projecting upward from the table I at a distance from the two rollers 2 and 3. The transmission from thebevel gear I to the upper driven roller is obtained by a vertical shaft I I driven by engagement of a bevel gear [2 at its lower end with the first mentioned bevel gear 1. A horizontal driven shaft I3 disposed in the horizontal arm 9 carries at one end a bevel gear I4 in engagement with a bevel gear I5 fixed to the upper end of the vertical shaft II. At the forward end of the horizontal shaft I3 is fixed another bevel gear it which engages a bevel gear I! fixed to the upper end of a two-part vertical shaft. The latter shaft comprises a hollow upper part I 8 and a lower part I9 adapted to slide therein and connected thereto by splines so that the two parts rotate together. The upper roller 2 is fixed to a shaft 26 carried in a bearing assembly 2| yieldingly mounted on compression springs 22 and capable of limited vertical-movement. A bevel gear 23 on the rearward end of the shaft is engaged by a bevel gear 24 fixed to the lower part I9 .of the two-part vertical shaft. A compression spring 25 behind the last mentioned bevel gear 24 maintains that gear in engagement with the bevel gear'23 during vertical movement of the upper roller 2. The upper and lower rollers 2 and 3 form between them the gap through which the material is passed by the driving action of those rollers on the material. A desired pressure may be applied by means of a lever 26 attached to the compression springs 22 associated with the upper roller, and by means of this lever the upper roller 2 may be lifted out of engagementwith the lower roller 3.

The lower roller 3 is formed with two electrodes 27 and 28 in the manner described in the specification of United Kingdom Application No. 30,418/45. The body of the roller is made of insulating materialand each of the electrodes 2'! and 28 is a metallic surface extending over an outer portion of the roller surface and radially inwards for a short distance on the corresponding side of the roller. The electrodes 21 and 28 are connected by side spring contacts 29 and 30 respectively to the terminals of a high frequency oscillator 3|. The upper roller 2 acts as a third electrode, and also as the pressure roller to press together the layers of thermoplastic material arranged between the two rollers. When under the influence of the high frequency alternating electric stress in the material between the rollers, the contacting surfaces are heated to a soft adhesive state, the pressure of the upper roller 2 presses them together so that they coalesce along the line of treatment. The driven rollers 2 and 3 carry the material steadily forward to form a seam.

The motor 4 is a directcurrent operated machine; the direct current supply is over the tWo lines 32 and 33, through a rotary variable rheostat 31, and over the three lines 34, 35, and 36 to the motor. The variable rheostat 3'! permits control of the voltage applied to the motor armature, and thereby controls the speed of the motor. The supply to the (oscillator is obtained'from a source of alternating currentover two lines 38 and 39 to a variable transformer 40, and from the-transformer to the oscillator over two lines 4 4| and 42. By adjustment of the transformer 40, the output voltage from the oscillator to the roller electrodes may be controlled. A common rotatable shaft 43 couples together the rotatable parts of the variable transformer 40 and the variable rheostat 31, a variable gear 44 being arranged in the coupling to the variable transformer. A foot-operated pedal 45 is connected through a linkage 46 to a rack-and-pinion drive 47 whereby rotation of the shaft 43 may be effected. A tension spring 48 facilitates the proper control of the shaft by the pedal 45. In the one extreme position when the pedal 46 is completely released, the mechanism of the adjustable members 40 and 31 may be arranged to interrupt the supply to the motor '4 and oscillator 3!.

When the materials to be joined involve a straight run through the machine, the speed of the motor may be increased by operating the pedal 45. At the same time the voltage applied to the electrodes from the oscillator 3| will also be increased, so that the rate of heating of the material will increase as required by its shorter time of passage between the rollers 2 and 3. When, due to the presence of turns and other features, it is necessary to reduce the speed of the rollers by releasing the pedal, the voltage across the electrodes will fall correspondingly. The relation between rates of variation of voltage and speed is pre-set by means of a hand control 49 of the variable gear 44 in the coupling 43 between the variable members 31 and 40. This relation will be pre-set, before commencement of the work, in accordance with the particular conditions, for instance, the nature andthickness of the material and the degree of heating required at the surfaces to be joined. Once preset, the particular relation will be automatically effective-throughout the range of control of the variable members 31 and 40, until again changed by hand.

It is preferred to use a direct current motor and to exert the control solely or primarily by operating on the voltage applied to the armature of that motor. The field of the motor is independently excited, that is to say it is not under control simultaneously with'the armature volt-- age. It may be a permanent magnet. The armature voltage is adjusted by the control so as to obtain an approximately constant torque, that'is approximately constant current at all speeds. It is preferable to provide a series winding on the field through which the armature current, or a proportion of it, passes, acting in such a sense as to prevent drop of speed with increase of mechanical load of the motor, or even to produce an increase of speed when the load increases and also to prevent increase of speed when the mechanical load falls off, or even to produce a decrease. This is found advantageous for dealing with local load variations such as occur at the step up or down from one thickness of material to another due to the change in the number of layers for instance, where no manipulated control change is made. The advantage of this automatic speed control in maintaining stability of working will be recognised on noting that a large part of the resistance to the movement of the rolls driven by the motor is due to the plasticity of the materials while passing between the rolls (increasing as the plasticity increases). Accordingly, if a rise of speed occurs without any simultaneous manipulative control of the heating effect the temperature reached in the material while passing between the rolls falls. Accordingly, the plasticity falls and the resistance to movement of the rollers falls so that the speed tends further to increase. This tendency is corrected by the effect of compounding of the motor.

The high frequency oscillator may be of the form described in the specification of United States application Serial No, 702,219, filed October 9, 1946, now Patent No. 2,469,990, issued 10, 1949, in which the output voltage is variable by means of a mechanically movable device incorporated in the oscillator construction. In such case, the single member for controlling the conditions in accordance with the present invention will be adapted to adjust simultaneously the speed controller for the rollers and the movable device incorporated in the oscillator.

What we claim as our invention is:

In a machine for joining superimposed layers of thermo-pla-stic material as along a seam by subjection of the contacting surfaces of the material to heating by a high frequency alternating electric field during movement of the material between pressure roller electrodes, an electric motor drive for at least one of said roller electrodes to impart said movement of the material, a variable speed-controller for said motor, an oscillator connected with and adapted to supply said alternating electric field between said roller electrodes, a variable oscillator-output controller for varying the intensity of said field, coupling means connecting together said speed controller REFERENCES CITED ihe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,023,316 Hurwitz Apr. 16, 1912 2,391,086 Crandell Dec. 18, 1945 FOREIGN PATENTS Number Country Date 118,453 Australia May 11, 1944 159,570 Great Britain Feb. 24, 1921 OTHER REFERENCES Plastics, September 1944, pages 30 and 32.

Radio Sealing, Wireless World, January 1945, pa e 29.

Plastics, September 1945, page 138.

Modern Packaging, May 1946, pages 120, 121. 

